Excessively high pressure in an operating cylinder of an internal combustion engine may cause damage to the engine pistons, cylinder heads, and other components. Peak firing pressure is affected by the combustion process and the conditions of the incoming combustion air. In addition, the operation of a turbo-charger increases peak firing pressure by increasing the temperature and pressure of the incoming air.
Internal combustion engines, and especially diesel engines, encounter a variety of operational conditions ranging from extreme cold at sea level to high temperatures at high altitudes. These conditions may induce various engine parameters to exceed designed engine limits, for example, peak firing pressure (PFP), turbocharger speed (TS), and preturbine temperature (PTT). More specifically, the parameters are more susceptible to being exceeded when the engine is running at full load at extreme ambient temperature and/or altitude conditions.
There is also a continued demand for improved performance of diesel engines, in terms of fuel economy, component loading, power output, and reduced emissions. To facilitate optimized engine performance, conditions of combustion within the internal combustion engine should be controlled. However, engine designs are limited because of the extremes of environmental conditions under which an engine must operate. For example, cylinder PFP may become too high when an engine is operating during cold days and when the inlet air temperature is low, thus generating excessive stress on engine components. Alternatively, cylinder exhaust temperatures may become too high when the engine is operated during hot days and when the inlet air temperature is very high, thus causing turbocharger damage due to overheating and overspeed.
U.S. Pat. No. 6,557,347 discloses methods and apparatus for controlling peak firing pressure for turbo-charged diesel engines. The method includes determining an allowable peak firing pressure, determining an actual peak firing pressure, and comparing the two firing pressures to control the operation of a turbocharger for controlling peak firing pressure. The rotational speed of the turbocharger is varied to vary intake pressure and hence combustion. A controller continuously monitors intake air manifold pressure and fuel injection timing and outputs a signal to the motor-generator driving the turbocharger. This method reduces engine torque output and is applicable only globally to all the engine cylinders equally.
What is needed in the art is a method and apparatus for controlling peak firing pressure in an internal combustion engine that does not substantially reduce output torque and that can control peak firing pressure in individual cylinders of the engine.
It is a principal object of the present invention to control peak cylinder pressure in an internal combustion engine.